Assessment of linear-scale indices for perimetry in terms of progression in early glaucoma

AbstractCurrently, global indices that summarize the visual field combine sensitivities on a logarithmic (decibel) scale. Recent structure–function models for glaucoma suggest that contrast sensitivity should be converted to a linear scale before averaging across visual field locations, to better relate sensitivity with the number of surviving retinal ganglion cells (RGCs). New indices designed to represent the number of RGCs already lost are described. At least one was found to be a significantly better predictor of subsequent rate of change than traditional Mean Deviation (p=0.014) in participants with glaucomatous optic neuropathy. Issues concerning the creation of optimal global indices are discussed

Prediction Accuracy of the Dynamic Structure-Function Model for Glaucoma Progression Using Contrast Sensitivity Perimetry and Confocal Scanning Laser Ophthalmoscopy

PURPOSE: The purpose of this study was to determine whether combining a structural measure with contrast sensitivity perimetry (CSP), which has lower test-retest variability than static automated perimetry (SAP), reduces prediction error with 2 models of glaucoma progression. METHODS: In this retrospective analysis, eyes with 5 visits with rim area (RA), SAP, and CSP measures were selected from 2 datasets. Twenty-six eyes with open-angle glaucoma were included in the analyses. For CSP and SAP, mean sensitivity (MS) was obtained by converting the sensitivity values at each location from decibel (SAP) or log units (CSP) to linear units, and then averaging all values. MS and RA values were expressed as percent of mean normal based on independent normative data. Data from the first 3 and 4 visits were used to calculate errors in prediction for the fourth and fifth visits, respectively. Prediction errors were obtained for simple linear regression and the dynamic structure-function (DSF) model. RESULTS: With linear regression, the median prediction errors ranged from 6% to 17% when SAP MS and RA were used and from 9% to 17% when CSP MS and RA were used. With the DSF model, the median prediction errors ranged from 6% to 11% when SAP MS and RA were used and from 7% to 16% when CSP MS and RA were used. CONCLUSIONS: The DSF model had consistently lower prediction errors than simple linear regression. The lower test-retest variability of CSP in glaucomatous defects did not, however, result in lower prediction error

Individual differences in the shape of the nasal visual field

AbstractBetween-subject differences in the shape of the nasal visual field were assessed for 103 volunteers 21–85years of age and free of visual disorder. Perimetry was conducted with a stimulus for which contrast sensitivity is minimally affected by peripheral defocus and decreased retinal illumination. One eye each was tested for 103 volunteers free of eye disease in a multi-center prospective longitudinal study. A peripheral deviation index was computed as the difference in log contrast sensitivity at outer (25–29° nasal) and inner (8° from fixation) locations. Values for this index ranged from 0.01 (outer sensitivity slightly greater than inner sensitivity) to −0.7 log unit (outer sensitivity much lower than inner sensitivity). Mean sensitivity for the inner locations was independent of the deviation index (R2<1%), while mean sensitivity for the outer locations was not (R2=38%, p<0.0005). Age was only modestly related to the index, with a decline by 0.017 log unit per decade (R2=10%). Test-retest data for 21 volunteers who completed 7–10 visits yielded standard deviations for the index from 0.04 to 0.17 log unit, with a mean of 0.09 log unit. Between-subject differences in peripheral deviation persisted over two years of longitudinal testing. Peripheral deviation indices were correlated with indices for three other perimetric stimuli used in a subset of 24 volunteers (R2 from 20% to 49%). Between-subject variability in shape of the visual field raises concerns about current clinical visual field indices, and further studies are needed to develop improved indices

Color matches in diseased eyes with good acuity: detection of deficits in cone optical density and in chromatic discrimination

Reduced foveal cone optical density in diseased eyes with normal acuity can affect color matches. Using field diameters of 1 ± , 2 ± , 4 ± , and 8 ± , we measured mean color-match midpoints and match widths in patients who had good acuity and who exhibited three categories of eye disease: hereditary macular degeneration (n 12), retinitis pigmentosa (n 19), and glaucoma (n 18). Results were compared with those for normal observers of comparable ages. Mean color-match midpoints were abnormal only for the population with hereditary macular degeneration, indicating a reduction in cone optical density in the central 4 ± . Mean color-match widths were enlarged for both hereditary macular degeneration and retinitis pigmentosa, a result consistent with a reduction in the number of foveal cones

Surface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical evolution, and outflow

We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem) to test current understanding of regional sources, chemical evolution, and export of NOx. The boundary layer NOx data provide top-down verification of a 50% decrease in power plant and industry NOx emissions over the eastern United States between 1999 and 2004. Observed NOx concentrations at 8–12 km altitude were 0.55 ± 0.36 ppbv, much larger than in previous U.S. aircraft campaigns (ELCHEM, SUCCESS, SONEX) though consistent with data from the NOXAR program aboard commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NOx and increases upper tropospheric ozone by 10 ppbv. Simulating ICARTT upper tropospheric NOx observations with GEOS-Chem requires a factor of 4 increase in modeled NOx yield per flash (to 500 mol/ flash). Observed OH concentrations were a factor of 2 lower than can be explained from current photochemical models, for reasons that are unclear. A NOy-CO correlation analysis of the fraction f of North American NOx emissions vented to the free troposphere as NOy (sum of NOx and its oxidation products) shows observed f = 16 ± 10% and modeled f = 14 ± 9%, consistent with previous studies. Export to the lower free troposphere is mostly HNO3 but at higher altitudes is mostly PAN. The model successfully simulates NOy export efficiency and speciation, supporting previous model estimates of a large U.S. anthropogenic contribution to global tropospheric ozone through PAN export

A model for fire‐induced sediment yield by dry ravel in steep landscapes

Sediment flux from hillslopes to channels commonly increases following wildfires, with implications for the carbon cycle, river habitats, and debris-flow hazards. Although much of this material is transported via dry ravel, existing ravel models are not applicable to hillslopes with gradients greater than the angle of repose, which can constitute the majority of mountainous terrain. To fill this knowledge gap, we develop a continuity model for sediment storage by vegetation dams on steep hillslopes to predict sediment yields following wildfire. The maximum volume of sediment stored prior to wildfire is set to be a function of vegetation density, the capacity of plants to impound sediment, and the contributing hillslope area. Time is required after fire to establish vegetation and replenish hillslope sediment storage, which introduces vegetation regrowth rate, soil production rate, and fire recurrence interval as important variables that affect ravel yield. Model results for the San Gabriel Mountains, California, predict that sediment yield can increase by several orders of magnitude following fire. These results are consistent with field data of ravel yield (~30 mm per contributing area of hillslope in 5 months) we collected following the 2009 Station Fire, as well as postfire sediment flux recorded by 93 debris basins. In contrast to previous work, our model shows that heightened postfire sediment yields can be explained by a change in hillslope sediment storage independent of major changes in the soil production rate and landscape form over geomorphic timescales

Complementary Patents and Market Structure

Many high technology goods are based on standards that require several essential patents owned by different IP holders. This gives rise to a complements and a double mark-up problem. We compare the welfare effects of two different business strategies dealing with these problems. Vertical integration of an IP holder and a downstream producer solves the double mark-up problem between these firms. Nevertheless, it may raise royalty rates and reduce output as compared to non-integration. Horizontal integration of IP holders solves the complements problem but not the double mark-up problem. Vertical integration discourages entry and reduces innovation incentives, while horizontal integration always benefits from entry and innovatio